1. Field of Invention
The present invention relates to an adhesive. More particularly, the present invention relates to a pressure-sensitive emulsion adhesive for over-laminating films, the fabrication method and the use thereof.
2. Description of Related Art
In general, the over-laminating film tapes can be applied to protect the prints of hot transfer printing, ink-jet printing, planography, gravure printing or letterpress from the damages of sun and moist. There are two types of over-laminating film tapes. For the first type of the over-laminating tapes, the structure of the tape includes a stacked structure of a substrate (generally biaxially oriented polypropylene film), an adhesive and a mold-release paper. During application, the tape is adhered to the object after peeling off the mold-release paper. The second type of over-laminating tapes has a three-layered structure of a substrate, an adhesive and a mold-release agent, which is directly applied and adhered to the object.
For the first type of the over-laminating tapes, the adhesion between the adhesive and the mold-release paper should be weak so as to be peeled easily. Generally, for the fabrication of the tape, the mold-release paper is coated with the adhesive, oven-dried and then attached to the substrate (coating transfer method). For this type of the over-laminating tapes, the mold-release paper has to be peeled off before the tape is adhered to the target object, which increase the production costs and is environmental unfriendly due to the disposal of the mold-release papers.
For the second type of the over-laminating tapes, one side of the substrate is coated with the mold-release agent (mold-release layer) and the other side of the substrate is coated with the adhesive, without using the mold-release paper. The adhesion of the mold-release layer relative to that of the adhesive layer should be carefully controlled, so that no white lines (peeling marks) are present if applied. When the mold-release agent is a silicon series mold-release agent, incomplete bridging may occurs and the mold-release agent is transferred to the surface of the glue, thus deteriorating the physical properties or transparency. Moreover, the silicone series mold-release agent is expensive. If the mold-release agent is a non-silicon series mold-release agent, problems of non-uniformity exist and unstable adhesion may result in the mold-release agent being transferred to the surface of the glue.
On the other hand, if the adhesive is directly coated to the surface of the substrate to form the over-laminating tapes without using the mold-release agent, the adhesion is stable and no white lines are present when applied, thus obtaining the over-laminating tapes of low costs and high quality.
The adhesives used for such over-laminating tapes includes emulsion type rubber series adhesives, emulsion type acrylic series adhesives, solvent type acrylic series adhesives and non-solvent type adhesives. The acrylic series adhesives are widely adopted for having good weather durability, adhesion, stability over time, and transparency. Compared with the acceptance of the emulsion type acrylic series adhesives in recent days, the solvent type acrylic adhesives are more expensive and may cause impacts to the ecology for containing organic solvents.
However, the conventional emulsion type acrylic series adhesives also have the disadvantages of poor waterproofness, easily turning yellow, higher occurrence of white lines and less adhesion in involution. Thus, for wider application, these problems need to be solved.